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Aspetti fisici della radioterapia moderna - II: Treatment planning, IMRT, protoni

Agenzia Provinciale per la Protonterapia Trento, Italy. Aspetti fisici della radioterapia moderna - II: Treatment planning, IMRT, protoni. Marco Schwarz schwarz@atrep.it. 23 Settembre 2010. Treatment Planning in 3D CRT. 3D CRT. Target defined in soft tissues on CT images

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Aspetti fisici della radioterapia moderna - II: Treatment planning, IMRT, protoni

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  1. Agenzia Provinciale per la Protonterapia Trento, Italy Aspetti fisici della radioterapia moderna - II: Treatment planning, IMRT, protoni Marco Schwarz schwarz@atrep.it 23 Settembre 2010

  2. Treatment Planningin 3D CRT

  3. 3D CRT • Target defined in soft tissues on CT images • Higher target/OAR doses than in 2D CRT • 3D Treatment planning • Safety margins must be considered while designing treatment field • ICRU 50(1993) and ICRU 62(1999) set the standard for dose planning and dose reporting reference volumes.

  4. PTV concept: pros • Forced people to explicitely incorporate geometrical uncertainties into treatment planning • Very appropriate tool for CRT: not too simple, not too complex. CTV = Clinical Target Volume (visible + microscopic disease) PTV = Planning Target Volume

  5. ‘Margin recipes’ Analytical solution for spherical targets (van Herk 2000) Derived/verified with simulations for real cases (e.g. Stroom 1999, Van Herk 2002) as a function of population-based data on geometrical uncertainties

  6. Different 'recipes'according to the desired probability level PTV planning= same dose prescription for all points above a given probability of presence for target cell

  7. PTV: cons • Use of accurately defined margins still quite rare • Dose homogeneity in the PTV became a must more for technical than for clinical reasons • N.B. IGRT mostly aims at reducing PTV margins without radically changing PTV-based RT techniques • Most important: the PTV concept works only if three assumptions are valid:

  8. PTV - playing by the rules The PTV is a tool for dose planning and dose reporting. There are three underlying assumptions: 1. The dose distribution is invariant for (small) translations and rotations 2. The margins are chosen appropriately as a function of the geometrical uncertainties one wants to compensate for 3. The dose distribution in the PTV is as homogeneous as possible. Condition1 is granted using photons, 2 and 3 must be ensured using correct planning practices.

  9. CTV OAR + = PTV expansion ? CTV OAR As if one should prefer homogeneous doses in the wrong PTV instead of heterogenous doses in the right PTV

  10. Treatment planning in IMRT

  11. More degrees of freedom More need to know what you want CRT IMRT

  12. How to tell a machine what we want from it ?

  13. Still struggling with TP in IMRT Inst.1 Inst. 2 Inst. 3 Inst. 4 Inst. 5 Adapted from Das et al, JNCI 2007

  14. In IMRT si hanno molti più gradi di libertà che in CRT, troppi per poter essere gestiti ‘a mano’. • Gli scopi del trattamento devono essere espressi in un linguaggio comprensibile tanto dall’uomo quanto dalla macchina L’ottimizzazione in IMRT è la gestione via macchina di una serie di obiettivi intrinsecamente in contraddizione.

  15. Funzione di costo • Traduzione quantitativa delle caratteristiche del piano di trattamento in termini di • Obiettivi di dose (e.g. Dmin, Dmax) • Intenti del trattamento (e.g. controllare la dose vs. massimizzarla/minimizzarla) • Trattamenti precedenti • Informazioni biologico/funzionali • Informazioni geometriche (e.g. errori di set-up) • Parametri di erogazione • …

  16. The objective cost function 1. Evaluator Quantifies a relevant feature of the plan 2. Modifier A function f of the difference between the actual (E) and the desired (E0) value of the evaluator Dmean Dmin/Dmax DVHpoint # segments treatment time plan robustness …

  17. 3-step IMRT treatment planning 1. Fluence optimization Cost function minimization Up to 10^4 ‘beamlets’ Dose calc: fast but not very accurate 2. Segmentation Mechanical and dosimetrical MLC parameters are included Deterioration of the dose distribution 3. Final dose calculation No reoptimization Dose calculations: slower, but more accurate than in step 1.

  18. Aperture based treatment planning 1. Initial fluence optimization 2. Initial Segmentation 3. Tuning of a deliverable plan Taking benefit of degeneracy --> More efficient delivery Less computational burden = Possibility of using accurate dose algorithms

  19. What do we talk about when we talk about ? Patient specific QA

  20. Don’t forget the big picture Huq et al, IJROBP 2008 71(1) Supp.

  21. 2-D dosimetry + gamma analysis What is patient specific in this approach? The beam setting Which aspect of the treatment chain is evaluated? The head model In most cases, field by field analysis Some techniques require whole treatment verification (e.g. VMAT)

  22. Monte Carlo dose calculation (Tübingen) Main advantages 1)It solves the main dosimetric problem of IMRT dose calculation algorithms (source model) 2)Combined with hardware QA, it allows to come back to separate hw e sw QA, as in CRT

  23. Planning CT (3D) EPID treatment image (2D) Planning dose (3D) EPID portal dose (2D imager plane) select mid-plane slice back-projection Planning dose (2D patient mid-plane) EPID dose (2D patient mid-plane) -evaluation In-vivo dosimetry(NKI) separate fields, 2D Courtesy B. Mijnheer

  24. Dose-based corrections protocols? Planning CT + Planned dose CBCT + In vivo dosimetry Gamma analysis: dose errors Vs anatomy changes McDermott, R&O2008

  25. Delivery

  26. Delivery

  27. Tecniche ad arco. Perché? • Aumento numero di campi >> aumento gradi di libertà • Migliore conformazione della dose • In caso di target concavi migliore risparmio degli OAR • Erogazione più veloce e riduzione movimenti intra-fraction • Molti parlano inoltre di migliore efficienza e riduzione MU, ma l’affermazione è discutibile From De Neve, in “Image-guided IMRT”, Springer Ed. 2007

  28. Time/efficiency

  29. Treatment complexity vs monitor unit s=1-Dmax/Dpresc Bakai et al, PMB 2003

  30. 2-step IMRT treatment planning 1. Fluence optimization Cost function minimization Up to 10^4 ‘beamlets’ Dose calc: fast but not very accurate 2. Segmentation Mechanical and dosimetrical MLC parameters are included Deterioration of the dose distribution 3. Final dose calculation No reoptimization Dose calculations: slower, but more accurate than in step 1.

  31. Aperture based treatment planning 1. Initial fluence optimization 2. Initial Segmentation 3. Tuning of a deliverable plan Taking benefit of degeneracy --> More efficient delivery Less computational burden = Possibility of using accurate dose algorithms

  32. Cone Beam Dose erogata in una singola/multipla rotazione del gantry Durante la rotazione la fluenza è modulata: - Variazione forma del campo(movimento lamelle MLC) - Variazione dei pesi dei campi (variazione di intensità) Fan Beam Dose erogata grazie ad un fan beam che ruota continuamente in concomitanza alla traslazione del lettino Durante la rotazione la fluenza è modulata: - Variazione forma del campo - Variazione dei pesi dei beamlets Tomoterapia seriale/elicoidale Tecniche Conformal Arc, AMOA, IMAT, VMAT

  33. IMRT (Angoli fissi) IMAT (Archi multipli) VMAT Single arc

  34. Tomoterapia Il gantry ruota per 360° creando 51 proiezioni Modulazione ottenuta variando il tempo di On/Off per ogni lamella Velocità di rotazione del gantry e tempo di trattamento dipendono da: dose di prescrizione, lunghezza target, dose rate

  35. Single/Few Arc(s) vs TOMO

  36. Prostata HT e IMAT: distribuzioni comparabili; IMAT: erogazione più veloce IMAT: riduzione dose integrale Canale Anale HT: migliore qualità piani; migliore copertura e omogeneità target; migliore risparmio genitali H&N HT: migliore qualità piani gradiente di dose più elevati Solid line: IMAT

  37. Interplay effects Bortfeld et al, PMB 2002 Could we solve it by adding a margin ? No (Not completely) Is it that bad ? It depends

  38. Intrafraction (‘interplay’) effects 1fr 30 fr 1fr 30 fr sw s&s10 s&s20 Jiang et al, PMB 2003

  39. New treatment modalities

  40. Heavier ions(?) HDR 'Conventional' XRT Tomotherapy IMXT Tomorrow's ideas 'Conventional' p+ Radiation delivery technologies

  41. IMPT 3DCRT TOMO Gy % 0% Dose 35%Dose 10% Dose Where would we like to use p+ ? In principle, for all patients In practice, whenever dose sparing at all dose levels could make the difference

  42. The Bragg peak

  43. Protons vs photons – Version 2

  44. 0.5 0.2 0.5 1.0 0.5 1.0 0.2 1.0 0.2 0.4 1.0 0.4 1.0 1.0 1.0 0.5 0.2 Protons vs photons – version 3 Fotoni Protoni

  45. 3D modulation + Steep dose fall off = More degrees of freedom Protons vs photons – version 4 X p+ +

  46. Protoni vs. Fotoni – caso pediatrico IMRT IMPT G. Fava - ATreP

  47. IMRT IMPT

  48. IMRT IMPT Sezione assiale con aree di basse dosi

  49. Dosimetric effects of geometrical uncertainties No errors 5mm setup 5mm setup 10 mm respiration 10mm setup M. Engelsman - MGH

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